Cap wielding the hammer? nah, I'm good on that. But I always envisioned a scene where Cap is laying on the ground next to the hammer and casually hands it to Thor before getting up and going back to the fighting. Then after a second or two, Thor does a double-take, like a "what the hell?" kind of moment. I don't think they need to show Cap worthy of lifting Mjolnir in the sequel, but I would like to see it adressed at some point in an Avengers movie. As a Cap fan, I think it would be an awesome scene in general, and really lend to the character for the GA to know he's one of the few worthy to lift it.